/*

 * Copyright 2020-2026 The OpenSSL Project Authors. All Rights Reserved.

 *

 * Licensed under the Apache License 2.0 (the "License").  You may not use

 * this file except in compliance with the License.  You can obtain a copy

 * in the file LICENSE in the source distribution or at

 * https://www.openssl.org/source/license.html

 */

/*

 * RSA low level APIs are deprecated for public use, but still ok for

 * internal use.

 */

#include "internal/deprecated.h"

#include "internal/nelem.h"

#include <openssl/crypto.h>

#include <openssl/evp.h>

#include <openssl/core_dispatch.h>

#include <openssl/core_names.h>

#include <openssl/rsa.h>

#include <openssl/params.h>

#include <openssl/err.h>

#include <openssl/proverr.h>

#include "crypto/rsa.h"

#include "internal/cryptlib.h"

#include "internal/fips.h"

#include "prov/provider_ctx.h"

#include "prov/providercommon.h"

#include "prov/implementations.h"

#include "prov/securitycheck.h"

#include "providers/implementations/kem/rsa_kem.inc"

static OSSL_FUNC_kem_newctx_fn rsakem_newctx;

static OSSL_FUNC_kem_encapsulate_init_fn rsakem_encapsulate_init;

static OSSL_FUNC_kem_encapsulate_fn rsakem_generate;

static OSSL_FUNC_kem_decapsulate_init_fn rsakem_decapsulate_init;

static OSSL_FUNC_kem_decapsulate_fn rsakem_recover;

static OSSL_FUNC_kem_freectx_fn rsakem_freectx;

static OSSL_FUNC_kem_dupctx_fn rsakem_dupctx;

static OSSL_FUNC_kem_get_ctx_params_fn rsakem_get_ctx_params;

static OSSL_FUNC_kem_gettable_ctx_params_fn rsakem_gettable_ctx_params;

static OSSL_FUNC_kem_set_ctx_params_fn rsakem_set_ctx_params;

static OSSL_FUNC_kem_settable_ctx_params_fn rsakem_settable_ctx_params;

/*

 * Only the KEM for RSASVE as defined in SP800-56b r2 is implemented

 * currently.

 */

#define KEM_OP_UNDEFINED -1

#define KEM_OP_RSASVE 0

/*

 * What's passed as an actual key is defined by the KEYMGMT interface.

 * We happen to know that our KEYMGMT simply passes RSA structures, so

 * we use that here too.

 */

typedef struct {

    OSSL_LIB_CTX *libctx;

    RSA *rsa;

    int op;

    OSSL_FIPS_IND_DECLARE

} PROV_RSA_CTX;

static const OSSL_ITEM rsakem_opname_id_map[] = {

    { KEM_OP_RSASVE, OSSL_KEM_PARAM_OPERATION_RSASVE },

};

static int name2id(const char *name, const OSSL_ITEM *map, size_t sz)

{

    size_t i;

    if (name == NULL)

        return -1;

    for (i = 0; i < sz; ++i) {

        if (OPENSSL_strcasecmp(map[i].ptr, name) == 0)

            return map[i].id;

    }

    return -1;

}

static int rsakem_opname2id(const char *name)

{

    return name2id(name, rsakem_opname_id_map, OSSL_NELEM(rsakem_opname_id_map));

}

static void *rsakem_newctx(void *provctx)

{

    PROV_RSA_CTX *prsactx;

    if (!ossl_prov_is_running())

        return NULL;

#ifdef FIPS_MODULE

    if (!ossl_deferred_self_test(PROV_LIBCTX_OF(provctx),

            ST_ID_ASYM_CIPHER_RSA_ENC))

        return NULL;

#endif

    prsactx = OPENSSL_zalloc(sizeof(PROV_RSA_CTX));

    if (prsactx == NULL)

        return NULL;

    prsactx->libctx = PROV_LIBCTX_OF(provctx);

    prsactx->op = KEM_OP_RSASVE;

    OSSL_FIPS_IND_INIT(prsactx)

    return prsactx;

}

static void rsakem_freectx(void *vprsactx)

{

    PROV_RSA_CTX *prsactx = (PROV_RSA_CTX *)vprsactx;

    RSA_free(prsactx->rsa);

    OPENSSL_free(prsactx);

}

static void *rsakem_dupctx(void *vprsactx)

{

    PROV_RSA_CTX *srcctx = (PROV_RSA_CTX *)vprsactx;

    PROV_RSA_CTX *dstctx;

    if (!ossl_prov_is_running())

        return NULL;

    dstctx = OPENSSL_zalloc(sizeof(*srcctx));

    if (dstctx == NULL)

        return NULL;

    *dstctx = *srcctx;

    if (dstctx->rsa != NULL && !RSA_up_ref(dstctx->rsa)) {

        OPENSSL_free(dstctx);

        return NULL;

    }

    return dstctx;

}

static int rsakem_init(void *vprsactx, void *vrsa,

    const OSSL_PARAM params[], int operation,

    const char *desc)

{

    PROV_RSA_CTX *prsactx = (PROV_RSA_CTX *)vprsactx;

    const BIGNUM *e = NULL;

    int protect = 0;

    if (!ossl_prov_is_running())

        return 0;

    if (prsactx == NULL || vrsa == NULL)

        return 0;

    if (!ossl_rsa_key_op_get_protect(vrsa, operation, &protect))

        return 0;

    if (!RSA_up_ref(vrsa))

        return 0;

    RSA_free(prsactx->rsa);

    prsactx->rsa = vrsa;

    /*

     * Reject the trivial public exponent e <= 1. The FIPS module enforces the

     * full SP 800-56B §6.4.1.1 constraints via ossl_fips_ind_rsa_key_check()

     * below; non-FIPS callers wanting the complete §6.4.2 vetting can use

     * EVP_PKEY_public_check().

     */

    RSA_get0_key(prsactx->rsa, NULL, &e, NULL);

    if (e == NULL || BN_cmp(e, BN_value_one()) <= 0) {

        ERR_raise(ERR_LIB_PROV, PROV_R_INVALID_KEY);

        return 0;

    }

    OSSL_FIPS_IND_SET_APPROVED(prsactx)

    if (!rsakem_set_ctx_params(prsactx, params))

        return 0;

#ifdef FIPS_MODULE

    if (!ossl_fips_ind_rsa_key_check(OSSL_FIPS_IND_GET(prsactx),

            OSSL_FIPS_IND_SETTABLE0, prsactx->libctx,

            prsactx->rsa, desc, protect))

        return 0;

#endif

    return 1;

}

static int rsakem_encapsulate_init(void *vprsactx, void *vrsa,

    const OSSL_PARAM params[])

{

    return rsakem_init(vprsactx, vrsa, params, EVP_PKEY_OP_ENCAPSULATE,

        "RSA Encapsulate Init");

}

static int rsakem_decapsulate_init(void *vprsactx, void *vrsa,

    const OSSL_PARAM params[])

{

    return rsakem_init(vprsactx, vrsa, params, EVP_PKEY_OP_DECAPSULATE,

        "RSA Decapsulate Init");

}

static int rsakem_get_ctx_params(void *vprsactx, OSSL_PARAM *params)

{

    PROV_RSA_CTX *ctx = (PROV_RSA_CTX *)vprsactx;

    struct rsakem_get_ctx_params_st p;

    if (ctx == NULL || !rsakem_get_ctx_params_decoder(params, &p))

        return 0;

    if (!OSSL_FIPS_IND_GET_CTX_FROM_PARAM(ctx, p.ind))

        return 0;

    return 1;

}

static const OSSL_PARAM *rsakem_gettable_ctx_params(ossl_unused void *vprsactx,

    ossl_unused void *provctx)

{

    return rsakem_get_ctx_params_list;

}

static int rsakem_set_ctx_params(void *vprsactx, const OSSL_PARAM params[])

{

    PROV_RSA_CTX *prsactx = (PROV_RSA_CTX *)vprsactx;

    struct rsakem_set_ctx_params_st p;

    int op;

    if (prsactx == NULL || !rsakem_set_ctx_params_decoder(params, &p))

        return 0;

    if (!OSSL_FIPS_IND_SET_CTX_FROM_PARAM(prsactx, OSSL_FIPS_IND_SETTABLE0,

            p.ind_k))

        return 0;

    if (p.op != NULL) {

        if (p.op->data_type != OSSL_PARAM_UTF8_STRING)

            return 0;

        op = rsakem_opname2id(p.op->data);

        if (op < 0)

            return 0;

        prsactx->op = op;

    }

    return 1;

}

static const OSSL_PARAM *rsakem_settable_ctx_params(ossl_unused void *vprsactx,

    ossl_unused void *provctx)

{

    return rsakem_set_ctx_params_list;

}

/*

 * NIST.SP.800-56Br2

 * 7.2.1.2 RSASVE Generate Operation (RSASVE.GENERATE).

 *

 * Generate a random in the range 1 < z < (n – 1)

 */

static int rsasve_gen_rand_bytes(RSA *rsa_pub,

    unsigned char *out, int outlen)

{

    int ret = 0;

    BN_CTX *bnctx;

    BIGNUM *z, *nminus3;

    bnctx = BN_CTX_secure_new_ex(ossl_rsa_get0_libctx(rsa_pub));

    if (bnctx == NULL)

        return 0;

    /*

     * Generate a random in the range 1 < z < (n – 1).

     * Since BN_priv_rand_range_ex() returns a value in range 0 <= r < max

     * We can achieve this by adding 2.. but then we need to subtract 3 from

     * the upper bound i.e: 2 + (0 <= r < (n - 3))

     */

    BN_CTX_start(bnctx);

    nminus3 = BN_CTX_get(bnctx);

    z = BN_CTX_get(bnctx);

    ret = (z != NULL

        && (BN_copy(nminus3, RSA_get0_n(rsa_pub)) != NULL)

        && BN_sub_word(nminus3, 3)

        && BN_priv_rand_range_ex(z, nminus3, 0, bnctx)

        && BN_add_word(z, 2)

        && (BN_bn2binpad(z, out, outlen) == outlen));

    BN_CTX_end(bnctx);

    BN_CTX_free(bnctx);

    return ret;

}

/*

 * NIST.SP.800-56Br2

 * 7.2.1.2 RSASVE Generate Operation (RSASVE.GENERATE).

 */

static int rsasve_generate(PROV_RSA_CTX *prsactx,

    unsigned char *out, size_t *outlen,

    unsigned char *secret, size_t *secretlen)

{

    int ret;

    size_t nlen;

    /* Step (1): nlen = Ceil(len(n)/8) */

    nlen = RSA_size(prsactx->rsa);

    if (out == NULL) {

        if (nlen == 0) {

            ERR_raise(ERR_LIB_PROV, PROV_R_INVALID_KEY);

            return 0;

        }

        if (outlen == NULL && secretlen == NULL)

            return 0;

        if (outlen != NULL)

            *outlen = nlen;

        if (secretlen != NULL)

            *secretlen = nlen;

        return 1;

    }

    /*

     * If outlen is specified, then it must report the length

     * of the out buffer on input so that we can confirm

     * its size is sufficient for encapsulation

     */

    if (outlen != NULL && *outlen < nlen) {

        ERR_raise(ERR_LIB_PROV, PROV_R_INVALID_OUTPUT_LENGTH);

        return 0;

    }

    /*

     * Step (2): Generate a random byte string z of nlen bytes where

     *            1 < z < n - 1

     */

    if (!rsasve_gen_rand_bytes(prsactx->rsa, secret, (int)nlen))

        return 0;

    /* Step(3): out = RSAEP((n,e), z) */

    ret = RSA_public_encrypt((int)nlen, secret, out, prsactx->rsa,

        RSA_NO_PADDING);

    if (ret <= 0 || ret != (int)nlen) {

        OPENSSL_cleanse(secret, nlen);

        return 0;

    }

    if (outlen != NULL)

        *outlen = nlen;

    if (secretlen != NULL)

        *secretlen = nlen;

    return 1;

}

/**

 * rsasve_recover - Recovers a secret value from ciphertext using an RSA

 * private key.  Once, recovered, the secret value is considered to be a

 * shared secret.  Algorithm is performed as per

 * NIST SP 800-56B Rev 2

 * 7.2.1.3 RSASVE Recovery Operation (RSASVE.RECOVER).

 *

 * This function performs RSA decryption using the private key from the

 * provided RSA context (`prsactx`). It takes the input ciphertext, decrypts

 * it, and writes the decrypted message to the output buffer.

 *

 * @prsactx:      The RSA context containing the private key.

 * @out:          The output buffer to store the decrypted message.

 * @outlen:       On input, the size of the output buffer. On successful

 *                completion, the actual length of the decrypted message.

 * @in:           The input buffer containing the ciphertext to be decrypted.

 * @inlen:        The length of the input ciphertext in bytes.

 *

 * Returns 1 on success, or 0 on error. In case of error, appropriate

 * error messages are raised using the ERR_raise function.

 */

static int rsasve_recover(PROV_RSA_CTX *prsactx,

    unsigned char *out, size_t *outlen,

    const unsigned char *in, size_t inlen)

{

    size_t nlen;

    int ret;

    /* Step (1): get the byte length of n */

    nlen = RSA_size(prsactx->rsa);

    if (out == NULL) {

        if (nlen == 0) {

            ERR_raise(ERR_LIB_PROV, PROV_R_INVALID_KEY);

            return 0;

        }

        *outlen = nlen;

        return 1;

    }

    /*

     * Step (2): check the input ciphertext 'inlen' matches the nlen

     * and that outlen is at least nlen bytes

     */

    if (inlen != nlen) {

        ERR_raise(ERR_LIB_PROV, PROV_R_BAD_LENGTH);

        return 0;

    }

    /*

     * If outlen is specified, then it must report the length

     * of the out buffer, so that we can confirm that it is of

     * sufficient size to hold the output of decapsulation

     */

    if (outlen != NULL && *outlen < nlen) {

        ERR_raise(ERR_LIB_PROV, PROV_R_INVALID_OUTPUT_LENGTH);

        return 0;

    }

#ifndef FIPS_MODULE

    /*

     * Reject clearly degenerate ciphertexts, c in {0, 1, n-1}.

     *

     * SP 800-56B Rev 2, 7.1.2.1 requires RSADP to enforce 1 < c < n-1.  In a

     * FIPS build that bound is applied by the RSADP primitive itself (see

     * crypto/rsa/rsa_ossl.c, guarded by FIPS_MODULE), where it is also needed

     * for KTS-OAEP; the primitive does not apply it in a non-FIPS build, so

     * enforce it here for RSASVE.  Raise the same errors as the primitive so

     * the behaviour matches in both builds; keep the two sites in step.

     */

    {

        const BIGNUM *n = RSA_get0_n(prsactx->rsa);

        BIGNUM *c = BN_new();

        BIGNUM *nminus1 = BN_new();

        int reason = 0;

        if (n == NULL || c == NULL || nminus1 == NULL

            || BN_bin2bn(in, (int)inlen, c) == NULL

            || BN_copy(nminus1, n) == NULL

            || !BN_sub_word(nminus1, 1)) {

            BN_free(c);

            BN_free(nminus1);

            return 0;

        }

        if (BN_ucmp(c, BN_value_one()) <= 0)

            reason = RSA_R_DATA_TOO_SMALL;

        else if (BN_ucmp(c, nminus1) >= 0)

            reason = RSA_R_DATA_TOO_LARGE_FOR_MODULUS;

        BN_free(c);

        BN_free(nminus1);

        if (reason != 0) {

            ERR_raise(ERR_LIB_RSA, reason);

            return 0;

        }

    }

#endif

    /* Step (3): out = RSADP((n,d), in) */

    ret = RSA_private_decrypt((int)inlen, in, out, prsactx->rsa, RSA_NO_PADDING);

    if (ret > 0 && outlen != NULL)

        *outlen = ret;

    return ret > 0;

}

static int rsakem_generate(void *vprsactx, unsigned char *out, size_t *outlen,

    unsigned char *secret, size_t *secretlen)

{

    PROV_RSA_CTX *prsactx = (PROV_RSA_CTX *)vprsactx;

    if (!ossl_prov_is_running())

        return 0;

    switch (prsactx->op) {

    case KEM_OP_RSASVE:

        return rsasve_generate(prsactx, out, outlen, secret, secretlen);

    default:

        return -2;

    }

}

static int rsakem_recover(void *vprsactx, unsigned char *out, size_t *outlen,

    const unsigned char *in, size_t inlen)

{

    PROV_RSA_CTX *prsactx = (PROV_RSA_CTX *)vprsactx;

    if (!ossl_prov_is_running())

        return 0;

    switch (prsactx->op) {

    case KEM_OP_RSASVE:

        return rsasve_recover(prsactx, out, outlen, in, inlen);

    default:

        return -2;

    }

}

const OSSL_DISPATCH ossl_rsa_asym_kem_functions[] = {

    { OSSL_FUNC_KEM_NEWCTX, (void (*)(void))rsakem_newctx },

    { OSSL_FUNC_KEM_ENCAPSULATE_INIT,

        (void (*)(void))rsakem_encapsulate_init },

    { OSSL_FUNC_KEM_ENCAPSULATE, (void (*)(void))rsakem_generate },

    { OSSL_FUNC_KEM_DECAPSULATE_INIT,

        (void (*)(void))rsakem_decapsulate_init },

    { OSSL_FUNC_KEM_DECAPSULATE, (void (*)(void))rsakem_recover },

    { OSSL_FUNC_KEM_FREECTX, (void (*)(void))rsakem_freectx },

    { OSSL_FUNC_KEM_DUPCTX, (void (*)(void))rsakem_dupctx },

    { OSSL_FUNC_KEM_GET_CTX_PARAMS,

        (void (*)(void))rsakem_get_ctx_params },

    { OSSL_FUNC_KEM_GETTABLE_CTX_PARAMS,

        (void (*)(void))rsakem_gettable_ctx_params },

    { OSSL_FUNC_KEM_SET_CTX_PARAMS,

        (void (*)(void))rsakem_set_ctx_params },

    { OSSL_FUNC_KEM_SETTABLE_CTX_PARAMS,

        (void (*)(void))rsakem_settable_ctx_params },

    OSSL_DISPATCH_END

};